Numerous inflated cushions have been proposed for varying the air pressure in selected portions of a cushion to change the areas of support over a period of time to improve comfort and blood circulation. These devices have been used on beds and wheelchairs to forestall or reduce skin breakdown in immobile or elderly patients. Skin breakdown can occur (usually at bony locations) when prolonged and uninterrupted sitting pressure reduces blood circulation below the level required to sustain tissue life. Breakdowns also can occur when a cushion does not provide adequate ventilation and causes the skin to be excessively moist and warm for prolonged periods.
Prior inflated cushioning devices have provided either passive or dynamic support for the body. While prior inflated devices have been useful, they have had some shortcomings. In some devices a leak can cause the cushion to collapse, rendering it ineffective. Some cushioning devices are not thick enough to fully contact and support the user's body contours without bottoming out. When cushion inflation pressure is increased to prevent bottoming out, the ability of the cushion to conform closely to the user's skin is reduced. As the cushion becomes more firm, its benefit to the user decreases. But if the cushion is made thicker to improve conformability, it tends to become unsteady and difficult for persons with impaired body balance to use. Moreover, as the cushion becomes more conformable it becomes more difficult for ventilating air to reach the skin and keep it cool and dry and thus increases the risk from skin maceration.
At the present time there are cushioning devices available which will support the body horizontally at pressures of about 10 millimeters of mercury and provide adequate ventilation. The fluidized bed is a prime example of one such device. But even fluidized devices cannot provide effective support for seated individuals in wheelchairs because there is insufficient seating area to reduce support pressures to the level of 10 millimeters of mercury advocated in medical literature for spinal cord injured persons. Sitting pressures at bony locations can be ten or thirty times higher than this amount and, except for cushion intervention, are the usual places where skin breakdown begins.
Cushion interventions which reduce the risk of skin breakdown generally involve providing increased conformability to reduce average sitting pressure (air or fluid filled passive cushions), contouring surfaces to support the user on the fleshier and non-bony parts of the sitting area which are less likely to develop pressure sores (foam composition passive cushions), conformable cushions with high heat acceptance capacity intended to delay heat build-up in the sitting area (gel filled passive cushions), dynamic cushions which continually shift sitting pressure to different parts of the resting surface to allow blood circulation and air circulation to be restored to all parts of the sitting area (alternating pressure cushions).
Medical authorities are in general agreement that an ideal cushion should not cause prolonged impairment of blood circulation to the tissues in the sitting area, should not cause the skin to become hot and moist, should provide stable support with postural and transfer benefits, should provide comfort, durability and convenience at an affordable price.
In one form the present invention provides an alternating pressure cushion which has the foregoing benefits to wheelchair cushion users without the limitations of earlier devices and concepts. The invention can also be used as a highly beneficial passive cushion. Moreover, it will not bottom out even if punctured.